The structural and electronic impact on the photophysical and biological properties of a series of CuI and AgI complexes with triphenylphosphine and pyrimidine-type thiones

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DOI: 10.1039/C4NJ02203C

Journal Name

Cite this: DOI: 10.1039/c0xx00000x

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ARTICLE TYPE

Structural and electronic impact on the photophysical and biological

I

properties of a series of Cu and Ag complexes with triphenylphosphine

and pyrimidine-type thiones.

a

b

c

Panagiotis A. Papanikolaou,*

Anastasios G. Papadopoulos,* Eleni G. Andreadou,

Antonios

a

d

c

a

5

Hatzidimitriou, Philip J. Cox, Anastasia A. Pantazaki and Paraskevas Aslanidis*

Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X

DOI: 10.1039/b000000x

I

Four Cu and three Ag mixed-ligand complexes containing a heterocyclic pyrimidine-type thione (pymtH = pyrimidine-2-thione or

dmpymtH = 4,6-dimethyl-pyrimidine-2-thione) and triphenylphosphine (PPh ) have been synthesized and structurally characterized. All

3

1

0

copper and two of the silver compounds, namely [Cu(PPh ) (pymtH) ]BF

(1), [Cu(PPh ) (pymtH)]BF

4

(2),

3

2

4

3

[

Cu(PPh ) (dmpymtH) ]BF (3), [Cu(PPh ) (dmpymtH)]BF (4), [Ag(PPh ) (pymtH)]NO (5) and [Ag(PPh ) (dmpymtH)]NO (6),

3

2

4

3

4

3

reveal a tetrahedral coordination environment while [Ag(PPh

3

)

2

(pymtH)]NO

3

(7) preferentially adopts a trigonal planar arrangement.

The stoichiometry of the isolated silver complexes does not always follow the respective stoichiometries of the synthetic procedures. The

photophysical properties of all the isolated products have been evaluated. In solution, a phosphine derived emission is detected while in

1

5

the solid state only [Cu(PPh

3 3 4

) (dmpymtH)]BF (4) emits from a state of different parentage. All of the complexes were also tested for in

vitro antibacterial activity against four bacterial strains and for anti-inflammatory activity by measuring lipoxygenase inhibition activity.

18-20

photophysical properties.

As has been shown, the emission

1

. Introduction

energy of these systems can be tuned through a thione-

modification related to the strength of the Cu–S bond while their

emitting state is readily assigned as MLCT on the basis of both

experimental and theoretical data. Further, a particular class of

copper(I) systems combining thiones and phosphine moieties

with intriguing photophysical properties have been reported by

5

6

7

0

5

0

5

0

5

2

3

4

0

5

0

5

0

5

The main characteristic of S,N-type ligands is the combination

1

a

of soft and hard sites that can selectively bind metal centers. In

this sense, heterocyclic thiones are regarded as potent

multifunctional donors for the development of extended or

higher nuclearity architectures. During the last few decades,

coinage metal complexes bearing this type of ligands have

attracted much research interest for their structural versatility.

More precisely and because of the ability of these molecules to

coordinate on the metal center in a monodentate or a bridging

mode, a large variety of halogenated copper(I) and silver(I)

compounds with heterocyclic thiones and aryl phosphines as

auxiliary ligands have been studied, revealling in most cases a

tetracoordinated mononeric or dimeric nature. Additionally, there

are some examples of tricoordinated species, particularly in the

presence of bulky phosphines while bidentate P-donor ligands

with small saturated carbon chains can favor the formation of

dinuclear, chelated or even more sophisticated structures.

2

21

Yam et al. The authors attributed a high energy emission

located at ca. 430-550 nm in solid samples to a ligand-centered

transition while in solution, a lower-lying (~ 600 nm) band with

1

b-d,2

3

lifetime in the range of μs arising from a LMCT excited state

governs the spectrum. A similar cluster-type compound has also

I

been reported, incorporating a sulfide ion connecting four Cu

centers, stabilized by diphosphine bridges. In this case both solid

state and fluid solution samples resulted in a long-lived yellow-

22

orange emission assigned to a mixed LMCT/MC state.

Analogous luminescent copper thiolate complexes have been

3

,4

23

studied by Langer et al. comprising a variety of nuclearities and

core geometries. As it was reported, the core structure of these

systems has a profound effect on their emissive properties which,

although not clear, seem to originate from a long-lived LMCT

excited state.

5

On the other hand, heterocyclic thione molecules attract

6

attention due to their relevance in biological systems. In

particular, the rationalization of the structural characteristics of

copper-thione mixed ligand species is of significant importance in

the design and understanding of analogues mimicking the blue

active site of redox active cuproproteins. In the same context,

both copper and silver complexes containing thione and/or

phosphines have revealed important antimicrobial and biological

Continuing our investigations on the chemistry of thione-

phosphine mixed-ligand coinage metal systems, we have

explored the structural and photophysical properties of a series of

7

I

Cu and Ag heteroleptic compounds containing the pyrimidine

skeleton (pymtH = pyrimidine-2-thione and dmpymt = 4,6-

dimethyl-pyrimidine-2-thione, Scheme I) in combination with

8-17

I

activity.

Recently, a series of Cu complexes incorporating

triphenylphosphine (PPh ). The complexes were all isolated as

3

heterocyclic thiones or thiolates in combination with aryl-

phosphines or phenanthroline have also revealed interesting

mononuclear species containing, in the case of copper, either two

phosphines and two thione molecules (Cu:PPh

3

:thione = 1:2:2) or

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three phosphines and one coordinated thione (Cu:PPh

:3:1), depending on the reaction stoichiometry. On the other

3

:thione = 45 According to Scheme I, a prototropic thiol-thione tautomerism

1

occurs for both sulfur containing ligands, although an incomplete

transfer of the migrating proton between the heterocyclic nitrogen

hand, silver complexes always contain one coordinated thione

irrespectively of the reaction stoichiometry. Despite the

detectable emission in solution, only one of the synthesized

2

5

and the exocyclic sulfur atom has been suggested. Several

assesements of the relative stability of the two forms have

5

0

5

complexes emits in the solid state from a state of different 50 revealed the prevalence of the thiol in the gas phase while, in the

parentage.

solid state, or in solution, the thione form appears to be more

Further, we examined the antibacterial activity of all the new

26-28

stable.

Theoretical studies on a similar system point towards a

complexes on both Gram positive and Gram negative bacteria as

well as their ability for anti-inflammatory activity by measuring

lipoxygenase inhibition activity. The 5-lipoxygenase (5-LOX)

pathway has been associated with a variety of inflammatory

diseases including asthma, atherosclerosis, rheumatoid arthritis,

pain, cancer and liver fibrosis. Several classes of 5-LOX

inhibitors have been identified, but only one drug, zileuton, a

small tautomeric energy gap as a result of the competition

between a thioamide resonance stabilization for the thione and a

typical aromatic stabilization for the thiol. The thioamide

1

29

5

6

7

5

0

5

0

5

resonance could also be a potent reason for maintaining the

planarity of the heterocyclic thione ring. In this framework semi-

empirical calculations on the two tautomers of pyrimidine-2-

1

25

thione revealed a bond localization in the heterocyclic ring of

2

4

redox inhibitor of 5-LOX, has been approved for clinical use.

the thione tautomer which points to a non- aromatic character. On

the contrary the thiol form appears to be typically aromatic.

In both tautomers of pymtH and dmpymtH, coordination may

occur either from the sulfur or/and the pyridine nitrogen atom of

the heterocyclic ring. In the present case, X-ray crystallography

shows the coordination of these ligands in the thione form as well

as their monodentate interaction with the metal center through the

sulfur atom. This is somewhat expected as the pre-coordinated

phosphines increase the soft character of the metal predisposing

the binding of the thione through its soft-base site. Considering

further the stereochemical demands imposed by the bulky

phosphines, the coordination of the thione through its sulfur

rather than its pyridine-type nitrogen atom should also be favored

because of a longer bond length which helps to reduce steric

repulsions in the coordination sphere. Further, the presence of the

thione form for the two ligands in the respective complexes is

supported by the comparison of experimental and theoretical data

for the Cip–S bond length, which are in very good agreement

2

. Results and Discussion

2

.1 Synthesis

The new compounds were prepared under atmospheric

conditions by mixing the respective materials in the desired

equivalent amounts. In the case of copper, a binary CH Cl

MeOH solvent mixture was used while methanol was found to

promote the crystallization process. In first step

[Cu(MeCN) ]BF is left to react in dichloromethane with the

appropriate amount of PPh in order to form an intermediate

complex assigned as [Cu(PPh (MeCN)4-x]BF (x = 2 or 3).

2

3

4

0

5

0

5

0

2

-

a

4

3

)

x

4

Treatment of the resulting solution with the corresponding thione

dissolved in methanol gives the final product. The complexes

were isolated as either orange or yellow solids for the 1:2:2 or

1

:3:1 stoichiometry respectively, and are microcrystalline, air

stable and diamagnetic in nature. In the case of silver only

methanol was used and the preparation involved the reaction of

2

6

when this tautomer is considered, as well as with literature data.

AgNO

3

with phosphine followed by the addition of thione

dissolved in methanol. The complexes are all yellow in colour,

diamagnetic and air stable. As it was revealed, the reaction of

8

0

2.2 Spectroscopic information

silver nitrate with PPh

coordinated complex bearing only one thione and two

phosphines, namely [Ag(PPh (pymtH)]NO (7) while the 1:3:1

ratio results in the expected [Ag(PPh (pymtH)]NO (5)

complex. For dmpymtH, only the [Ag(PPh (dmpymtH)]NO

6) complex was isolated regardless of the reaction ratio.

3

and pymtH in a 1:2:2 ratio affords a three

The infrared spectra of the prepared complexes show the

expected distinct and strong vibrational features attributed to the

phosphine moiety. These bands appear as a set of sharp peaks

3

)

2

3

-1

located around 695 and 517 cm revealing small shifts upon

3

)

3

6

,30

8

9

5

0

5

coordination to the metal center.

In all cases, a strong band

3

)

3

-1

located in the region 1602-1610 cm for pymtH-systems and at

618 cm for dmpymtH-systems can be assigned to the stretching

(

-1

1

vibrations of the –C=N– and –C=C– bonds of the thione ring. The

N

-1

same band appears in the free thiones at 1607 cm and 1624 cm

SH

for pymtH and dmpymtH, respectively, and is totally absent in

the phosphine spectrum. Its negligible variation upon

coordination can be attributed to changes in the electronic

structure of the heterocyclic ring imposed by the presence of the

metal center rather than coordination by the heterocyclic

pyridinic nitrogen atoms. The latter supports the binding of the

thione by the sulfur atom. Moreover, the spectra of the studied

compounds contain the usual four “thioamide bands” required by

the presense of the heterocyclic thione ligands in the regions

N

P

NH

N

NH

N

S

PPh3

pymtH

dmpymtH

-1 1b

Scheme I. Molecular structure and thione-thiole tautomeric equilibria for

the ligands used.

~1510, 1320, 1000 and 750 cm

overlapping partially with

1

00 neighbouring peaks. In addition, the lack of ν(SH) bands at ca.

2

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-1

2

500-2600 cm verifies the presence of the sulfur-ligand in its

thione form although the characteristic stretching frequency of

-

1

31,32

the –NH group in the 3150 cm region

Further for the copper complexes, the BF

is not clearly evident.

stretching appears as

-

4

-1

5

a strong peak at ~1060 cm . The nitrate absorption of the silver

complexes locates around 1337 cm .

-1

2

.3 X-ray structures

The single crystal structures of all the complexes were

1

0

determined. Crystallographic data are listed in Table S1 and

ORTEP views are depicted in Figures 1–7 where anions may

have been removed for clarity.

4

0

3 3 4

Figure 2. Perspective view of [Cu(PPh ) (pymtH)]BF (2).

Selected bond lengths (Å) and angles ( ): Cu1–S1=2.3902 (12),

Cu1– P1=2.3648 (11), Cu1–P2= 2.3726 (12), Cu1–P3=2.3334

o

(

11), S1–C1=1.691 (4), S1–Cu1–P1=95.17 (4), P1–Cu1–

P2=107.85 (4), P1–Cu1–P3=113.37 (4), S1–Cu1–P2=109.43 (5),

S1–Cu1–P3=110.78 (4), P2–Cu1–P3=117.86 (4), Cu1–S1–

C1=113.99 (16).

4

5

Figure 1. Perspective view of [Cu(PPh

3

)

2

(pymtH)

2

]BF

4

(1). Selected

o

bond lengths (Å) and angles ( ): Cu1–S1=2.4093 (9), Cu1– S2=2.3658

(10), Cu1–P1= 2.2838 (9), Cu1–P2=2.2888 (9), S1–C1=1.664 (3), S2–

C5=1.715 (3), S1–Cu1–S2=112.90 (3), S1–Cu1–P1=112.93 (3), S2–Cu1–

P1=106.07 (3), S1–Cu1–P2=99.93 (3), S2–Cu1–P2=102.36 (4), P1–Cu1–

P2=122.36 (3), Cu1–S1–C1=109.26 (11), Cu1–S2–C5=110.08 (11).

1

5

2

0

The geometrical characteristics of the copper(I) complexes 1–

4

are comparable to those of other mononuclear copper(I) species

tetrahedrally coordinated by thione and phosphine ligands. The

CuP core geometry in 1 and 3 is very similar to that of

Cu(py2SH)

2

S

2

3

34

[

2

(PPh

3

)

2

]NO

3

2 3 2 4

and [Cu(py2SH) (PPh ) ]ClO

2

3

5

0

5

with interbond angles around the central copper atom moderately

deviating from the idealized tetrahedral geometry. The somewhat

stronger distortion of the P–Cu–P angle can be accounted for by

the steric hindrance induced by the bulky phenyl-rings of the two

phosphine units. In this respect the tetrahedral arrangement in 2

and 4, each with three bulky phosphine ligands, appears to be

somewhat more regular as in 1 and 3.

Figure 3. Perspective view of [Cu(PPh

3

)

2

(dmpymtH)

2

]BF

4

(3). Selected

o

bond lengths (Å) and angles ( ): Cu1–S1=2.3350 (6), Cu1– S2=2.3815

(6), Cu1–P1= 2.3013 (5), Cu1–P2=2.2958 (5), S1–C37=1.711 (2), S2–

5

6

0

5

0

C43=1.700 (2), S1–Cu1–S2=119.434 (11), S1–Cu1–P1=101.24 (2), S2–

Cu1–P1=105.17 (2), S1–Cu1–P2=108.38 (2), S2–Cu1–P2=102.75 (2),

P1–Cu1–P2=120.97 (2), Cu1–S1–C37=112.70 (7), Cu1–S2–C43=110.03

(7).

Considering the bond distances, the most remarkable feature in

the structures of 1 and 3 is the quite large asymmetry in the two

individual Cu–S bond distances. Further, the Cu–P bonds in 2 and

4 are clearly larger than those in 1 and 3, probably due to steric

effects.

Similar to the copper complexes discussed above, the silver

nucleus in [Ag(PPh (pymtH)]NO (5) and

Ag(PPh (dmpymtH)]NO (6) is tetracoordinated with a P

3

)

3

[

3

)

3

S

ligand donor set. It is noteworthy that our previous studies with

thione/triphenylphosphine mixed-ligand complexes of silver(I)

show that AgNO

3

preferentially forms compounds with a

1

d,35

AgP S central core.

2

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in 5 and 4.795 Å in 6) is too large to warrant any kind of bonding

interaction.

Figure 4. Perspective view of [Cu(PPh

3

)

3

(dmpymtH)]BF

4

(4). Selected

o

bond lengths (Å) and angles ( ): Cu1–S1=2.3736 (11), Cu1– P1=2.3769

(10), Cu1–P2= 2.3698 (11), Cu1–P3=2.3418 (10), S1–C1=1.711 (4), S1–

Cu1–P1=93.83 (4), P1–Cu1–P2=108.13 (4), P1–Cu1–P3=113.80 (4), S1–

Cu1–P2=110.84 (4), S1–Cu1–P3=111.55 (4), P2–Cu1–P3=116.42 (4),

Cu1–S1–C1=115.42 (13).

5

3 3 3

Figure 6. A view of [Ag(PPh ) (dmpymtH)]NO (6). Selected bond

o

2

5

lengths (Å ) and angles ( ): Ag1–S1=2.6052 (11), Ag1–P1=2.5228 (10),

Ag1–P2= 2.5881 (10), Ag1–P3=2.5370 (11), S1–C1=1.695 (4), S1–Ag1–

P1=109.92 (4), S1–Ag1–P2=91.65 (4), S1–Ag1–P3=115.93 (4), P1–Ag1–

P2=113.67 (4), P1–Ag1–P3=106.38 (4), P2–Ag1–P3=106.38 (4), Ag1–

S1–C1=108.73 (15).

3

0

Figure 5. A view of [Ag(PPh

3

)

3

(pymtH)]NO

3

(5). Selected bond lengths

o

(Å ) and angles ( ): Ag1–S1=2.6310 (9), Ag1–P1=2.5054 (8), Ag1–P2=

2

.5349 (9), Ag1–P3=2.5626 (8), S1–C1=1.681 (4), S1–Ag1–P1=109.30

1

0

(3), S1–Ag1–P2=111.78 (3), S1–Ag1–P3=94.44 (3), P1–Ag1–P2=119.49

3), P1–Ag1–P3=113.27 (3), P2–Ag1–P3=105.73 (3), Ag1–S1–

C1=108.78 (13).

Figure 7. A view of [Ag(PPh

3

)

2

(pymtH)]NO

(Å ) and angles ( ): Ag1–S1=2.5701 (5), Ag1–P1=2.4480 (5), Ag1–P2=

.4415 (4), S1–C1=1.680 (2), S1–Ag1–P1=118.603 (18), S1–Ag1–

3

(7). Selected bond lengths

o

(

2

3

5

P2=113.294 (18), P1–Ag1–P2=127.817 (16), Ag1–S1–C1=89.34 (6).

A comparison of the structures of 5 and 6 with those of the

Compound 7 has been synthesized and characterized earlier in

the context of a study on mixed-ligand silver(I) compounds of

various heterocyclic thiones and its crystal structure is already

known. However, for the sake of completeness, we consider it

useful to include this compound in our present investigations.

1

5

corresponding copper counterparts 2 and 4 reveals an overall less

extented divergence of the interbond angles from the ideal

tetrahedral value, suggesting a better rearrangement of the bulky

ligands around the bigger silver cation. In both structures the non-

protonated nitrogen atom of the thione ligand is oriented towards

the metal center but the distance between the two atoms (3.552 Å

3

6a

4

0

2

The AgP S core in 7 is nearly planar with interbond angles

2

0

o

deviating slightly from the idealized value of 120 . As will be

4

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New Journal of Chemistry

I

shown further below, the exceptional formation of a tricoordinate

complex originates from electronic rather than from steric factors.

complexes. In the case of the Cu ion, such transitions are favored

I

by its strong reducing nature while the redox inertness of Ag

At this point it should be mentioned that the experimentally 45 does not allow for similar low-energy electronic excitations.

4

0

determined distance of 2.737 Å between the non-protonated N-

atom of the pymtH ligand and the metal ion, lies out of the

statistical upper limit of 2.72 Å already reported for a weak

Also, the absorption of the dmpymtH-systems is slightly

5

0

5

blueshifted compared to the respective pymtH-compound, as

shown in Table 1. This can be assigned to the destabilization of

the accepting thione-orbitals through a positive inductive effect

imposed by the methyl groups of the pyrimidine ring.

All of the synthesized compounds were tested for their ability

to emit both in the solid sate and in solution. After excitation in

the UV region (λexc = 300 nm) of an optically dilluted sample of

each complex in dichloromethane, a broad peak maximizing

around 480 nm is detected (Figure S3). This emission is not

observed when the samples are excited at longer wavelengths

I

36b

interaction between Ag and light donor atoms

and thus

5

6

7

0

5

0

5

0

5

typically excludes an even weak Ag-N bonding. This is evident

also from the retaining of an almost ideal trigonal planar

arrangement of the cation while in the case of a fourth, even

1

weak, metal-pymtH interaction,

a perceptible deformation

towards a tetrahedral stucture should be expected. Further, the

shorter metal-ligand bond lengths in 7 compared to 5 agree with a

2

more profound sp character for the metal center. The deviation

(λ_e_x_c> 350 nm) indicating that it results from a higher lying

1

of the electronic structure of the cation from the 18e rule can be

related to a substantial charge accumulation on the silver core as

it results from DFT calculations (vide infra).

excited state of the complexes. The appearance of this emission

in the same wavelength both for copper and silver complexes

typically excludes

a

MLCT character because of the

aforementioned different susceptibility of the two metals towards

oxidation. Additionally, the retaining of the emission in

acetonitrile, as has been observed, points against the MLCT

character for the emissive state. On the other hand and supposing

an effective steric protection of the metal center by the

coordinated phosphines, the emission energy of the complexes

accommodating three such ligands should be higher compared to

the rest of the systems. This is due to a more crowded

coordination sphere which would prevent structural

rearrangements and the stabilization of the excited state through

2.4 Photophysical studies

2

0

The electronic absorption spectra of all complexes in

dichloromethane reveal a strong band in the ultraviolet region and

a lower energy shoulder extending up to 430 or 480 nm for the

silver and copper derivatives, respectively (Figure 8 and Figure

*

S1). The high intensity peak can be assigned to intraligand π-π

2

5

transitions of the aromatic rings while the broad low-lying

absorption, located in the region of the free thiones chromophoric

band, can be assigned to a combination of thione intraligand and

charge transfer excitations (Figure S2). The charge transfer nature

4

1a

exciplex formation. Under the same excitation (300 nm), a

similar emission band is observed in a dichloromethane solution

4

1b

of triphenylphosphine indicating that the emitting state of the

complexes can be readily assigned as IL-PPh in nature (Figure

3

S3) or stemming from an uncoordinated phosphine moiety

because of a partial dissociation.

I

Table 1. Photophysical data of the synthesized Cu and Ag complexes in

the solid state and in dichloromethane.

a

b,c

d

Compound

λ

abs, nm

λ

em, nm

λ

em, nm

3

-1

(ε

abs, dm mol cm )

[

Cu(PPh

3

)

2

3

2

3

2

3

(pymtH)

(pymtH)]BF

(dmpymtH)

(dmpymtH)]BF

2

]BF

4

(1)

364(sh)

473

480

478

479

484

487

473

-

(

7331)

354(sh)

3590)

4

(2)

-

(

2

]BF

4

357(sh)

(6516)

352(sh)

(2829)

351(sh)

-

(

3)

Cu(PPh

4)

[

4

505

3

4

0

5

0

Figure 8. Normalized absorption spectra of [Cu(PPh

3) (blue) and [Cu(PPh (dmpymtH)]BF

dichloromethane. Normalized emission spectrum of PPh

Cu(PPh (dmpymtH)]BF (4) (green) in KBr disk after photoexcitation

3

)

2

(dmpymtH)

(4) (yellow) in

(black) and

2 4

]BF

(

3

)

3

4

[

Ag(PPh

(pymtH)]NO

3

(5)

(6)

-

3

(3473)

[

3

)

3

4

349(sh)

at 300 nm and 350 nm respectively.

(2565)

(dmpymtH)]NO

3

347

is supported by the calculated ε values reported in Table 1.

7

d

(7)

(3765)

Because of the phosphine propensity to act as an electron donor,

a

8

0

refers to the longest wavelength absorption in dichloromethane

the CT transitions involve a charge displacement from the latter

b

c

d

λ

exc = 300 nm, dichloromethane solution, KBr disk

moiety or the central metal region towards the acceptor empty π-

37-39

orbitals of the heterocyclic thione unit (MLCT/LLCT).

The

In the case of the free thiones in dichloromethane, only

^d^m^p^y^m^t^H^w^a^s^s^h^o^wⁿ^t^o^l^u^mⁱⁿ^e^s^c^e⁽^λexc = 350 nm) with a

MLCT character of the chromophoric absorption agrees well

with the blueshift observed for silver compared to copper

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Page 6 of 15

−1

maximum at 530 nm (Figure S2) while in the solid state, no

μg·mL . The minimum inhibitory concentration (MIC) values

appreciable emission was detected for pymtH or dmpymtH. On 60 obtained for each strain and each compound are presented in

the other hand, triphenylphosphine exhibits a broad band with

maximum at 428 nm after photoexcitation at 300 nm in KBr

(Figure 8). Concerning the metal complexes in the solid state,

only [Cu(PPh ) (dmpymtH)]BF (4) luminesces (λ_e_x_c= 350 nm)

Table 2.

5

0

5

0

5

0

5

0

5

0

Table 2 Antimicrobial activities of the complexes 1-7 evaluated by the

-

1

inhibitory concentration 50 (μg mL ).

3

4

with a strong and broad emission located at 505 nm (Figure 1).

By considering the similar photophysical behavior of the

phosphine and this complex in solution, the observed emission of

the latter in the solid state should be of a different parentage to

the one detected in dichloromethane. This can be ascribed to a

lower lying MLCT excited state, further supported by theoretical

data (see further below) as well as by the fact that the selected

excitation cannot populate any IL-phosphine-based excited states.

Additionally, the emission of the complex in the solid state

appears to be redshifted compared to the one observed in

solution. Since in the solid state energy loses are reduced because

of a more rigid environment, the lower emission energy of the

solid form can be assigned respectively to a lower energy

E. coli

S. aureus

(+)

B. cereus B. subtilis

(

-)

(+)

IC50

(+)

IC50

Compound

IC50

μg/mL)

IC50

(μg/mL)

(

(μg/mL)

1

2

3

4

5

[

Cu(MeCN)

4

]BF

(pymtH)

(pymtH)]BF

(dmpymtH)

4

>100

28

-

>100

Cu(PPh

3

)

2

3

2

]BF

4

(1)

(2)

]BF

-

26

-

4

24

13

2

4

(

3)

[Cu(PPh

Ag(PPh

3

)

3

(dmpymtH)]BF

(pymtH)]NO

(dmpymtH)]NO

4

(4)

-

12

8

24

8

12

9

[

3

(5)

7.5

3.5

18-20

emitting state compared to solution. As already reported

similar assignments concerning the character of the emissive state

have been reported. In the present case, the steric bulkiness of

[Ag(PPh

3

9

8

10

(6)

[

Cu(PPh

3 3 4

) (dmpymtH)]BF (4) accounts for the narrow Stokes

[

Ag(PPh

3

)

2

(pymtH)]NO

3

(7)

25

17

24

18

+

shift. On the other hand and compared to the typical [Cu(NN) ] -

and [Cu(NN)(PP)] -type chromophores,

2

+

7d,41

6

7

8

5

0

5

0

the coordination of

Among the three silver compounds, excellent antibacterial

activity is observed for the tetrahedral complexes 5 and 6, while

the effectiveness of the trigonal planar one (compound 7) is much

less pronounced.

Contrary to that, the antibacterial activities of the four

copper(I) complexes 1–4 are quite different. Thus, while

compound 1 is found to be inactive, the other three show

selective antibacterial activity only against certain types of Gram-

solely soft bases on the metal center can justify the relatively high

energy absorption and emission bands, through stabilization of

I

the Cu oxidation state.

The [Cu(PPh

3 3 4

) (dmpymtH)]BF (4) complex presents the

same structural characteristics with the one reported by Langer et

2

3

I

al. bearing two independent Cu centers. In both cases, each

metal core is coordinated by three phosphorus and one sulfur

atom resulting to the same CuP S-type chromophore.

3

positive bacteria strains. In particular, [Cu(PPh ) (dmpmt)]BF

4

(compound 4) exhibits significant antibacterial activity against all

three Gram-positive bacteria strains, with a particularly low IC

Additionally, and as in our case, the dinuclear complex of Langer

3

2

3

et al,. does not emit in solution after photoexcitation in the

visible region while this compound and

Cu(PPh ) (dmpymtH)]BF (4) both emit in the solid state at the

50

−1

value of 12 μg·mL against S. aureus and B. subtilis, while

Cu(PPh ) (dmpymtH) ]BF (compound 3) displays an equally

[

3

4

[

same wavelength (505 nm). Further, and according to reference

data, Langer et al., attribute the emission of the dinuclear

complex to a longlived LMCT state related to the strong electron-

donating ability of the coordinated thiolate. On the other hand,

3

2

4

good activity only against S. aureus. It should be noted that no

antibacterial activity was detected for the free pymtH, dmpymtH

and PPh used as ligands.

3

4

1

such states are known to be generally non-emissive, while, in

Cu(PPh (dmpymtH)]BF (4) the thione ligand is accomodated

[

3

)

3

4

2

.6 In vitro anti-inflammatory activity

in its neutral form thus limiting its donor ability. In our opinion

and based on DFT results presented below, it is safer to attribute

the solid state emission of [Cu(PPh ) (dmpymtH)]BF (4) to an

Lipoxygenases (LOX) catalyse the regio- and stereo-specific

8

9

5

0

5

dioxygenation of polyunsaturated fatty acids containing 1(Z),

(Z) pentadiene system, to form hydroperoxides, which are

3

4

MLCT state. The lack of lifetime data do not allow for a clear

assignement of the total spin although the participation of a

leukotriene precursors. The dioxygenase activity of LOX displays

rather broad substrate specificity. The inhibitory concentration

3

MLCT is largely expected. The emission is quenched in solution

(

IC ) values of the tested compounds, and nordihydroguaiaretic

50

either by air oxygen or structural rearrangements after

photoexcitation.

acid (NDGA) towards soybean LOX after 7 min of incubation are

given in Table 3 and the effect of concentration on lipoxygenase

inhibition activity for the [Cu(PPh ) (pymtH) ]BF

4

3

2

(1) is

2

.5 Evaluation of antibacterial activity

depicted in Figure 9.

Screening of the anti-inflammatory activity of the complexes

under investigation showed that most of them exhibited a

moderate inhibition of lipoxygenase activity with the exception of

The antimicrobial activities of the complexes 1-7 (average of

5

three measurements) were estimated by monitoring the growth of

certain Gram-positive (B. subtilis, B. cereus, S. aureus) and

Gram-negative (E. coli) bacterial srtains in the presence of

various concentrations of these complexes, ranging from 0 to 100

[

3 2 2 4

Cu(PPh ) (pymtH) ]BF (1), which, with an IC50 of 176 μM, is the

most prominent inhibitor among the evaluated compounds.

6

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New Journal of Chemistry

calculations on the free thiones and the respective cationic

4

3

complexes. The PBE1PBE functional was selected along with

4

the SDD basis set for the description of the metal core and the

4

5

Table 3. In vitro evaluation of anti-inflammatory activity based on

6-31G(d) basis sets for light atoms. The structure of the two

30 ligands was optimized both in the thione and the thiol form either

in the gas phase or in solution. In the latter case a rather nonpolar

solvent (dicloromethane) or a solvent of medium polarity

5

lipoxygenase activity inhibition.

Compound

Inhibition of lipoxygenase activity

IC50 (μΜ)

(

methanol) was considered. The obtained geometrical and

[

Cu(MeCN)

4

]BF

(pymtH)

(pymtH)]BF

(dmpymtH)

4

440

176

energetic parameters for the two forms in the assumed media are

35 summarized in Table S2. Despite the fact that for the isolated

ligands in the vacuum state the thiol form appears to be more

stable (by 2.8 kcal mol for pymtH and 1.4 kcal mol for

dmpymtH), in solution the two molecules adopt their thione form.

Cu(PPh

3

)

2

3

2

]BF

4

(1)

(2)

]BF

4

> 500

360

-1

2

4

-1

(

3)

This is more stable than the thiol tautomer by ca. 7.2 kcal mol in

-1

4

0

dichloromethane and 8.6 kcal mol in methanol both for pymtH

and dmpymtH. Consequently, it is expected that in the solvent

system used for the preparation of the present complexes, the

sulfur-containing ligands will mainly occur in their thione form in

agreement with the solid state experimental as well as previously

reported

[

Cu(PPh

Ag(PPh

3

)

3

(dmpymtH)]BF

(pymtH)]NO (5)

(dmpymtH)]NO

4

(4)

> 500

460

3

[

(

Ag(PPh

3

> 500

6)

26-28

4

5

findings.

An intriguing point is related to the stoichiometry of the

[

Ag(PPh

3

)

2

(pymtH)]NO

3

(7)

247.25

1.3

I

resulting Ag compounds. In all of the Cu complexes the

respective ligands are accommodated in the isolated structures in

accordance to the molecular ratios used in the synthetic

NDGA

Among the silver (I) complexes, [Ag(PPh

3

)

2

(pymtH)]NO

3

(7) 50 procedure. However, treatment of two equivalents of

displayed the most potent inhibition on lipoxygenase activity.

This finding might be related to the number of PPh₃moieties

present in each case. The same effect was obtained among the

copper (I) compounds, where again the strongest activity was

found for complexes 1 and 3, also possessing only two PPh₃

ligands. Thus, this result suggests that the bulkiness of the third

triphenylphosphine with one equivalent of silver salt and two

equivalents of pymtH yields the tricoordinated trigonal planar

+

1

0

[Ag(PPh

3

)

2

(pymtH)] (7) complex instead of the expected

+

(pymtH)

2

]

complex. Similarly, the reaction of

results to the formation of the

55 AgNO

with dmpymtH and PPh

3

+

tetrahedral [Ag(PPh (dmpymtH)] (6) cation irrespectively of

3 3

)

PPh turns probably the compounds less accessible to the active

site or generally to the surface of the enzyme lipoxygenase in

order to inhibit effectively the enzyme.

the reaction stoichiometry. In order to explore the reasons leading

to this irregular behavior we optimized the structures of both the

isolated and the expected systems containing the sulfur ligands in

3

1

5

I

6

7

8

0

5

0

5

0

their thione form. Analogous calculations for the isolated Cu

complexes were also performed. Since in this case no

differentiations in the reaction products were observed, the

obtained results will be only discussed briefly and in line with the

respective silver compounds.

Figure

9.

Effects

of

various

concentrations

of

2

0

[Cu(PPh ) (pymtH) ]BF (1) on lipoxygenase inhibition activity.

3 2 2 4

2

.7 Theoretical Results

.7.1 Geometrical features

In order to understand some marked structural and electronic

Figure 10. Optimized structure of the trigonal planar

2

+

[

Ag(PPh

3

)

2

(pymtH)] (7) cation revealing the non-favoring orientation of

the heterocyclic pyridine-type N atom for coordination on the metal

center.

2

5

features of the compounds under study we performed DFT

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Page 8 of 15

S and Ag–P bond lengths respectively, while the P-Ag-P bond

Geometrical parameters of the studied Ag cations are given in 60 angle is by ~7 larger compared to the largest value of the S–Ag–

I

o

Tables S3 and S4. After optimization the three-coordinated

complex retains its trigonal planar configuration with a slight

deviation of the sulfur atom from the plane defined by the two

phosphorus atoms and the metal center amounting to 0.106 Å and

P angles. This can be assigned to steric repulsions exerted

between the bulky phosphines although the presence of the

methyl groups on the thione rings restricts the distance between

5

0

5

0

5

0

5

0

5

0

5

the two PPh ligands compared to the respective pymtH complex.

3

o

two slightly unequivalent P–Ag–S angles of 114.4 and 113.1 . 65 The dihedral angle defined by the P–Ag–P and S–Ag–S planes

o

The two Ag–P bond lengths also show a small difference

probably assigned to strereochemical demands resulting from the

orientation of the pyrimidine ring towards one of the coordinated

phosphines in the optimized structure. Both of these bond lengths

amounts to 77.12 while upon coordination a minor elongation of

the C –S bonds (~ 0.06 Å) is assigned to the coordination of the

ip

1

2

3

4

5

sulfur atoms on the metal center. An analogous tetrahedral

geometry is obtained after optimization of the isolated

+

as well as that of the Ag–S bond (2.598 Å) are in good agreement 70 [Ag(PPh ) (dmpymtH)] (6) cation. In contrast to what is

3

with experimental data. On the other hand, the distance of the

metal ion from the heterocyclic pyridine-type nitrogen atom is

found at 3.261 Å precluding any strong bonding interaction

between the two centers (Figure 10). As can be seen by the

observed in the respective pymtH complexes, the Ag–S bond

length in the present case is shorter by 0.03 Å than the one found

+

in the [Ag(PPh ) (dmpymtH) ] . Nevertheless and despite the

3

2

stronger Ag–S interaction as expressed through the bond lengths,

comparison of geometrical data for the optimized structure of 75 the C –S bond of the present complex appears to be also

ip

pymtH in the vacuum state and the respective

shortened

compared

to

the

respective

bonds

in

+

[

Ag(PPh ) (pymtH)] (7) complex (Tables S2 and S3

[Ag(PPh ) (dmpymtH) ] . Further the three Ag–P bonds are

3 2

3

2

respectively), the coordination of the thione to the metal ion

through the exocyclic sulfur atom does not impose any severe

structural distortions to the heterocyclic ring resulting only in a

weak shortening of the Cip–Npyr and Cip–Nim bond lengths while

almost of equal length and P–Ag–P bond angles vary from ca.

o

110 to 118 .

80

2.7.2 Energetic assignments

an elongation of about 0.025 Å occurs for the C –S bond, related

ip

In order to investigate the aforementioned irrational behavior

of the reactions involving silver, we proceeded to estimate the

thermodynamic stability of the various products. According to

to the charge displacement towards the metal upon ligation.

I

3

Coordination of two pymtH and two PPh moieties on the Ag

+

cation towards the expected [Ag(PPh ) (pymtH) ] complex

3

2

I

8

9

5

0

5

thermochemical results for the reaction of Ag with pymtH, the

results to an optimized tetrahedral arrangement around the metal

center (Table S3). The two Ag–S and the two Ag–P bond lengths

differ by 0.008 Å and 0.034 Å respectively while the P–Ag–P

bond angle appears sustantially larger compared to the respective

S–Ag–P angles. An apparent difference also occurs in the bond

angles defined by each phosphorus atom, the silver core and each

of the two sulfur centers. The dihedral angle between the two P–

+

formation

of

tetrahedral

[Ag(PPh ) (pymtH) ]

is

3

2

thermodynamically more favored with computed reaction heats,

-

1

Δ H, of -128.17 kcal mol for the trigonal complex and -144.76

R

-1

kcal mol for the tetrahedral complex. The same term for

[Ag(PPh ) (pymtH)] (5) is estimated at -133.17 kcal mol . As

+

-1

3

I

far as it concerns the Ag -dmpymtH systems, formation of

+

-1

[

Ag(PPh ) (dmpymtH) ] is favored by ca. 10.75 kcal mol over

o

3

2

+

Ag–P and S–Ag–S planes is defined at 84.26 . As in the trigonal

[Ag(PPh

3

)

3

(dmpymtH)] (6) (Δ

respectively). Accordingly, although not isolated

R

H = -147.77 and -137.02 kcal

system no strong structural changes are observed on the thione

-1

mol

ring upon coordination with an elongation of the C –S bonds of

ip

experimentally, the Ag:PPh :thione = 1:2:2 cation appears to be

3

ca. 0.05 Å. Similarly coordination of three phosphines and one

pymtH molecule on the silver cation favours a tetrahedral AgP₃S

thermodynamically more preferable for both thione ligands.

Despite the inefficiency of thermochemical calculations to

rationalize the formation of the observed silver products, the data

chromophore unit isolated experimentally in the form of

+

[Ag(PPh

3

)

3

(pymtH)] (5). The optimized structure (Table S3)

are sufficient to explain the difference on the Ag:PPh :thione =

3

reveals three slightly different Ag–P bond lengths with P–Ag–P

1

00 1:2:2 reaction ratio product formation for the two thiones. More

precisely and for the above analogy, dmpymtH leads to the

o

bond angles varying between ca. 113 and 120 . The Ag–S bond

distance adopts a larger value compared to the two former cases

partially due to stereochemical repulsions stemming from the

+

formation of the tetrahedral [Ag(PPh ) (dmpymtH)] (6). When

3

+

pymtH is used instead, trigonal [Ag(PPh ) (pymtH)] (7)

3

2

phosphines. The difference of 0.189

Å

observed for

-1

+

complex is isolated which appears to be 5 kcal mol less stable

[

Ag(PPh ) (pymtH)] (7) and [Ag(PPh ) (pymtH)] (5) indicates

3 2 3 3

+

1

05 than the respective [Ag(PPh ) (pymtH)] (5) complex. As the

3

a weaker coordination of the thione in the latter system although

estimated difference lies on the limit of thermal energy (3-6 kcal

this is not shown by the C –S bonds which are approximately

ip

-1

mol ) stereochemical factors in the coordination shpere are

equal in length.

expected to govern the final product formation thus leading to a

less crowded trigonal planar conformation. In the case of

As mentioned above, reaction of dmpymtH with AgNO and

3

PPh

Ag(PPh

as well as that of the expected [Ag(PPh ) (dmpymtH) ]

3

always results in the isolation of the tetrahedral

+

110

dmpymtH, the same energy difference accounts for the isolation

[

3 3

) (dmpymtH)] (6) complex. The nature of this cation

+

of the more crowded tetrahedral [Ag(PPh

3

)

3

(dmpymtH)] (6)

3

2

-1

complex which appears to be 110.59 kcal mol more stable than

complex were also investigated by DFT calculations. Structural

data of the two optimized structures are given in Table S4. The

+

the respective trigonal [Ag(PPh

for the latter been estimated at only -26.43 kcal mol ).

3 2 R

) (dmpymtH)] complex (Δ H

-1

+

elusive [Ag(PPh ) (dmpymtH) ] species adopts a tetrahedral

3

2

1

15

Analogous findings are obtained by including entropic factors

in the above study. Further, in the case of copper, the calculated

coordination environment comprising two almost equivalent Ag–

8

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New Journal of Chemistry

I

thermochemical data are in agreement with the isolation of

preference for a trigonal planar Ag -pymtH complex over the

+

[Cu(PPh

3

)

2

(pymtH)

:thione = 1:2:2 reaction stoichiometry. The divergent

coordination behavior of silver, especially underlined by the 30 could block the ligation of a second pymtH species. In the same

2

] (1) and [Cu(PPh

3

)

2

(dmpymtH)

2

] (3) for

respective tetrahedral [Ag(PPh

3

)

2

(pymtH)

2

] complex cannot be

I

a Cu:PPh₃

attributed to an elusive Ag –N bonding interaction which

pyr

+

5

formation of a trigonal planar geometry, agrees with its known

high lability demonstrated in a variety of disproportionation and

context the isolation of the tetrahedral [Ag(PPh

complex accounts for the propensity of the [Ag(PPh

(7) unit to accommodate a fourth ligand. Since PPh

3 3

) (pymtH)] (5)

+

3

)

2

(pymtH)]

4

6

ligand scrambling reactions.

3

is bulkier

than pymtH, steric factors are quite unlikely to be held

responsible for preventing the formation of the

Ag(PPh ) (pymtH) ] entity.

3

4

5

6

7

5

0

5

0

5

0

5

0

+

[

3

2

In

the

optimized

structure

of

the

expected

+

Ag(PPh ) (pymtH) ] complex (Table S3), the two N atoms

3

2

pyr

are directed away from the metal core excluding any bonding

interaction while they retain the same charge as in the free thione.

A substantial electron density accumulation is observed on the

central atom which now appears with a minor positive charge of

HOMO

LUMO

+

0.019 charge units. This could be rationalized on the basis of a

less efficient π-back donation towards the heterocyclic thione ring

3

6a

compared to the trigonal planar system. By considering the

+

[

3 2

Ag(PPh ) ] fragment as the acceptor and pymtH as the donor

4

7

moiety upon coordination, a CDA analysis of the two structures

indeed reveals a larger back electron transfer (b) per thione ligand

+

in the case of the [Ag(PPh

3

)

2

(pymtH)] (7) complex (b = 0.296

vs 0.223 units). This in conjunction to a less crowded

stereochemical environment in the coordination sphere and a

more profound Ag–S electrostatic interaction as shown by the

calculated atomic charges, could support the formation of the

HOMO-1

LUMO+1

+

Figure 11. Selected FMOs of the [Cu(PPh

3

)

2

(pymtH)

2

] (1) cation.

+

trigonal planar [Ag(PPh ) (pymtH)] (7) complex in preference

3

2

+

to the respective tetrahedral [Ag(PPh ) (pymtH) ] complex. In

3

2

the same context, the uptake of an additional phosphine from the

I

Ag center in order to form the highly crowded

+

[Ag(PPh

3

)

3

(pymtH)] (5) complex can be related to an even

stronger π-back donation towards the thione ligand (b = 0.323) as

well as to an effective Ag–S electrostatic interaction according to

atomic charges. The weaker π-back transfer to each pymtH

HOMO

LUMO

+

moiety in [Ag(PPh ) (pymtH) ] is well exemplified by the equal

3

2

delocalization of either of LUMO and LUMO+1 over both these

units while in the rest of the complexes comprising two

coordinated thiones, each of the lowest virtual orbitals is mainly

confined to only one thione (see Table S8).

It should be noted that replacement of one thione in the

+

HOMO-1

LUMO+1

[Ag(PPh ) (pymtH) ] cation by a PPh molecule to give the

3

2

3

+

1

2

0

5

0

5

Figure 12. Selected FMOs of the [Cu(PPh

3

)

3

(pymtH)] (2) cation.

3 3

respective and stable tetrahedral [Ag(PPh ) (pymtH)] (5)

complex results in a more positive charge (+0.20) for the metal

center. In this regard, the additional triphenylphosphine can

stabilize the accumulated electron density on the metal core

through charge delocalization. This is better indicated by the

strong involvement of the phosphine parts on the HOMOs of both

I

By inspecting the NBO atomic charges of the Ag -pymtH

related systems (Table S7), it becomes obvious that upon

coordination there is a charge shift from the sulfur atom (-0.16

charge units for the free thione) and the two phosphorus atoms

(

+0.91 charge units in the free triphenylphosphine) towards the 75 the tetrahedral systems along with metal based AOs (Table S8).

metal center (-0.13 charge units for the S and +0.95 charge units

for the P atoms in the complex) with the latter aquiring a charge

of +0.29 units in the [Ag(PPh ) (pymtH)] (7) complex. An

analogous diminishing of electronic charge occurs for the iminic

nitrogen atom of the thione upon coordination (from -0.56 in the 80 [Ag(PPh ) (dmpymtH) ] complex can be assigned to the same

free thione to -0.54 in the Ag -complex) while an opposite sign

charge variation of ca. -0.02 units is observed for the pyridine-

type nitrogen atom (qNpyr = -0.46 in the free thione and -0.48 in

the complex). The latter finding denotes the lack of a Ag –N_p_y_r

On the other hand, the pyrimidine ring is related to the vacant

orbitals (LUMO) and thus cannot offer any charge relaxation on

the metal core. On a totally similar basis the preferential

+

3

2

+

formation of the [Ag(PPh ) (dmpymtH)] (6) complex over the

3

+

3

2

I

electronic factors described above and imposed by the

replacement of a thione moiety by a PPh₃ligand. The shape of

the FMOs (Table S8) of these two complexes also supports the

electronic stability offered by the presence of the phosphines

I

coordination interaction in the complex. In this respect the

This journal is © The Royal Society of Chemistry [year]

Journal Name, [year], [vol], 00–00 | 9

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DOI: 10.1039/C4NJ02203C

New Journal of Chemistry

Page 10 of 15

through electron density delocalization. Despite the low positive

charge of the metal center in both systems, the increase in the

number of the coordinated phosphines causes a respective

increase on its value by 100%.

5

+

Table 4. Selected principal singlet–singlet electronic transitions of the complex [Ag(PPh

3

)

2

(pymtH)] (7) calculated at the PBE1PBE/6-31G(d),SDD level

of theory.

Excitation

E/eV

λ/nm Orbital Nature

Character

OS, f

HOMO → LUMO, HOMO-1 → LUMO

HOMO-2 → LUMO, HOMO-4 → LUMO

2.930

3.523

423

352

4d_A_g/π_P_P_h

π_P_P_h→ π*₍_p_y_m_t_H₎

4d_A_g/π_P_P_h→ π*₍_p_y_m_t_H₎

π₍_p_y_m_t_H₎π*₍_p_y_m_t_H₎

3

→ π*₍_p_y_m_t_H₎

MLCT/LLCT

LLCT

0.0030

0.0262

3

HOMO → LUMO+1

HOMO-7 → LUMO

3.847

4.140

322

299

3

MLCT/LLCT

IL

0.0408

0.0010

→

HOMO-4 → LUMO+1, HOMO-2 → LUMO+1

HOMO → LUMO+2, HOMO-1 → LUMO+2

4.576

4.677

271

265

π_P_P_h

3

→ π*₍_p_y_m_t_H₎

LLCT

0.0259

0.0669

4d_A_g/π_P_P_h

3

→ π*₍_P_P_h₃₎

MLCT/IL

HOMO-1 → LUMO+3

HOMO → LUMO+5

4.767

4.832

260

257

→ 4d_A_g/π*₍_P_P_h₃₎

→ π*₍_P_P_h₃₎

MC/IL

0.2094

0.1007

MLCT/IL

3

0

sterically crowded environment in the 1:3:1 complex. This does

not hold in the same extent for the two related dmpymtH systems.

+

3 2

Figure 14. Experimental absorption spectrum of [Ag(PPh ) (pymtH)]

Figure 13. Predicted electronic transitions and participating MOs for the

(

7) cation along with the calculated excitation energies appearing as

+

1

0

[Ag(PPh

3

)

2

(pymtH)] (7) cation.

vertical lines.

3

5

2

.7.3 Electronic structure

In order to better clarify the electronic structure of the

In all cases the thione C=S bond lengths are found typically equal

and agree well with crystallographic data.

As can be seen in Figures 11 and 12 the highest occupied

orbital (HOMO) of both copper systems is of a d-σ character

synthesized compounds, we report DFT results for a copper and

+

1

2

5

0

5

a

silver cation, namely [Cu(PPh

3

)

2

(pymtH)

2

]

(1) and

+

40 comprising mainly contributions from the metal center d AOs and

[Ag(PPh ) (pymtH)] (7), on the basis of MO shapes and

3

2

+

the phosphine moieties. In the case of [Cu(PPh ) (pymtH) ] (1)

excitation energies. A similar discussion is also presented for the

3

2

+

there is an additional slight participation from the π-system of one

thione ligand. The same holds for HOMO-1 which retains a d-σ

nature and extends over the same molecular parts. The sulfur

atoms of the thiones also make some contributions to this orbital.

[

3 3

Cu(PPh ) (pymtH)] (2) cation as a means to probe differences

resuting from the coordination of a PPh₃moiety over a thione

ligand. MO shapes for all of the optimized systems of interest are

given in SI (Table S8) and are in agreement with the selected

examples.

4

5

On the other hand and in both cases the lowest virtual orbitals

*

(

LUMO and LUMO+1) can be assigned as π -MOs totally

As already mentioned, the coordinated sulfur-ligands have

been considered in their thione tautomeric form. The optimized

geometries of the selected systems along with structural

parameters are given in Tables S3 and S5 in SI. Concerning

located on the heterocyclic thiones and being almost degenerate

+

for the [Cu(PPh ) (pymtH) ] (1) complex. Considering that the

3

2

I

5

0

lowest energy excitations of the above Cu heteroleptic

complexes will mainly involve transitions between the

aforementioned MOs, it becomes apparent that their lowest lying

+

[

Cu(PPh ) (pymtH) ] (1) and [Cu(PPh ) (pymtH)] (2), a

3 2 2 3 3

substantial difference occurs to the Cu-S and one of the Cu-P

bond lengths for the two optimized geometries as a result of the

I

singlet excited state can be assigned as a mixed Cu -to-thione and

1

0

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New Journal of Chemistry

phosphine-to-thione charge transfer in nature (MLCT/LLCT).

rearrangement is significantly restricted. In this framework, time-

I

Figure 13 and Table 4 comprise the shapes of MOs and the 60 resolved X-ray diffraction studies on Cu complexes in the

predicted vertical electronic transitions for the trigonal planar

silver cation in its optimized structure. As in the case of copper

compounds, HOMO is of a d-σ character bearing substantial

contribution from the π-system of the two phosphines and smaller

but important participation of the metal center d AOs as well as 65 [Cu(PPh ) (dmpymtH)] (4) in the solid state, we performed TD-

3 3

from the thione sulfur atom. Similarly HOMO-1 retains the d-σ

crystalline phase revealed only modest alterations of dihedral

angles upon excitation with a concomitant diminishing of

5

1,52

5

0

5

0

5

0

5

reorganization energies.

Hence, in order to assign the emissive state of

+

DFT calculations assuming negligible structural variations of the

complex in the excited state. In this sense and by retaining the

ground state geometry of the system, the energy for the vertical

nature extending typically over the same molecular parts although

1

2

3

it mainly locates in the AgP S-core of the cation. The lowest

2

*

virtual orbitals (LUMO and LUMO+1) can be assigned as π -

S -T transition was estimated at 461 nm which is close to the

0 1

MOs totally located on the heterocyclic thione ring with 70 determined 505 nm emission wavelength. Energy deviations can

participation of the sulfur atom AOs. As is expected, the lowest

energy excitations will mainly comprise transitions between the

aforementioned FMOs. In this sense the lowest singlet excited

state of silver systems can be also described as being of a mixed

MLCT/LLCT character.

be attributed to the small, although expected, geometry relaxation

of the complex after photoexcitation. It should be pointed that the

proposed TD-DFT method for the prediction of the emission

energy gives, in this case, a rather unrealistic result (720 nm)

75 while the Δ-SCF energetic approximation assuming geometry

In Figure 14, a simulation of the experimental absorption

relaxation in the T state results in a 640 nm wavelength

1

+

spectrum of [Ag(PPh ) (pymtH)] (7) through TD-DFT

prediction. Consequently our approximation seems to offer a

realistic description of the de-excitation process and supports

further the assignement of the emissive state of

3

2

calculations is presented. The computed eigenvectors offer a

rather good description of the longer wavelength region with

three basic excitations (423, 352, 322 nm) corresponding to the 80 [Cu(PPh ) (dmpymtH)] (4) in the solid state as a MLCT.

shoulder over 320 nm. According to the shape of the involved

MOs (Table 2) these transitions are better assigned as

MLCT/LLCT in nature embarking from the metal center and the

phosphine moieties towards the vacant π-orbitals of the thione

heterocyclic ring. Higher energy excitations are also in accord

with experimental absorption bands and mainly comprise an

+

3

3. Conclusions

A new family of four heteroleptic tetrahedral Cu as well as

two tetrahedral and one trigonal planar Ag complexes, have been

I

8

9

5

0

5

synthesized and structurally characterized. The isolation of the

36a

latter complex confirms previous findings. In all cases the

MLCT/IL

character.

Similar

calculations

for

sulfur-ligands are coordinated on the metal center in

a

+

[Cu(PPh ) (pymtH) ] (1) also reveal a good representation of

3

2

monodentate mode through their thione-type atom.

S

the experimental absorption spectrum by the derived vertical

excitations and predict an MLCT/LLCT character for the lower

energy transition of the system (Figure S4). The above results

verify the quality of the selected level of theory on the description

of the electronic structure of all the systems included in the

present work.

Spectroscopic results along with theoretical data reveal an

MLCT/LLCT as the lowest singlet excited state of the systems.

Further, for all complexes in dichloromethane, a phosphine-

derived emission is detected while in the solid state,

[

Cu(PPh ) (dmpymtH)]BF (4) emits at 505 nm from a

MLCT/LLCT excited state.

3 3 4

3

Theoretical calculations were also performed in order to

2

.7.4 Emission wavelength prediction

rationalize the reasons leading to the unexpected stoichiometries

I

for two of the synthesized Ag -complexes. The non feasible

Further studies were undertaken in order to elucidate the nature of

+

isolation

Ag(PPh

of

[Ag(PPh ) (pymtH) ]

and

4

5

0

5

0

5

the emission observed for [Cu(PPh

3

)

3

(dmpymtH)] (4) in the

3

2

+

[

3

)

2

(dmpymtH)

2

]

cations may be explained by a

solid state. As already mentioned, this emission potently

3

1

00 predicted charge accumulation on the metal center which further

results in strong repulsive forces towards the thione-ligands. The

originates from a MLCT state. In this context, two theoretical

approximations have already been establised for the description

of the photophysics of transition metal complexes behaving as

^r^e^p^l^a^c^e^m^c^eⁿ^t^o^f^oⁿ^e^t^hⁱ^oⁿ^e^b^y^a^P^P^h3 molecule results to the

+

4

8

stable

[

tetrahedral

[Ag(PPh

3

)

3

(pymtH)]

(5)

and

triplet emitters. One relays on the estimation of the energetics

for the vertical T -S transition by calculating the energy

difference (Δ-SCF) between the fully optimized T state of the

system and its ground state (S ) retaining the T geometry. The

+

Ag(PPh ) (dmpymtH)] (6) cations where an electron spreading

3 3

1

o

1

05 towards the phosphine phenyl rings offers a charge relaxation on

the metal core. This observation could be related to a stronger

participation of the phosphine moieties on the high-lying

occupied MOs compared to the heterocyclic thione ring. In this

1

o

1

second method is more broadly applied and uses TD-DFT in

order to predict the vertical electronic excitation energy between

respect the non formation of the Ag:PPh :thione = 1:2:2

the closed-shell ground state of the system and its T state using

3

1

48-50

110 complexes can be attributed to electronic factors. On the other

hand the compensation between trigonal planar

Ag:PPh :thione 1:2:1) and Ag:PPh :thione 1:3:1

the T

1

structure.

a

In general terms both methods are based on the optimal T

1

(

=

a

=

geometry since the vertical emissive de-excitation process occurs

from this state, and usually refer to solution experimetal data

where the molecule can easily undergo stuctural changes in order

to obtain this geometry after photoexcitation. However, in the

solid state the molecule is rather constrained and structural

3

tetrahedral complex can be rationalized on the basis of

thermochemical data and steric demands.

I

1

15

Biological assesments showed that the two tetrahedral Ag

complexes are characterized by a strong antimicrobial activity,

Journal Name, [year], [vol], 00–00 | 11

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New Journal of Chemistry

Page 12 of 15

I

64

while Cu compounds show selective action only against certain 55 PLATON.

Tables for publication were prepared with

6

5

Gram-positive bacteria. On the other hand, only a moderate

activity towards lixygenase inhibition was revealed, directly

related to the bulkiness of the coordination sphere.

SHELXS97 and WinGX.

Crystal data and structure refinement parameters of 1–6 are

presented in Table 1. Illustrations were drawn by CAMERON.

6

Further details on the crystallographic studies as well as atomic

60 displacement parameters are given as Supporting Information in

the form of cif files. CCDC-1019197 (1), CCDC-1019194 (2),

CCDC-1018215 (3), CCDC-1019193 (4), CCDC-1019196 (5)

and CCDC-1019195 (6) containing the supplementary

crystallographic data for this paper. These data can be obtained

5

4. Experimental

4.1 Materials and measurements

The starting material [Cu(MeCN)

according to the proposed method. AgNO , triphenylphosphine,

pyrimidine-2-thione and 4,6-dimethyl-pyrimidine-2-thione were

used as received. Solvents of reagent grade were also used

without any prior purification or drying process. Elemental

analyses for C, H and N were performed with a Perkin-Elmer

4

]BF

4

was synthesized

5

3

6

5

free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or

from the Cambridge Crystallographic Data Centre, 12 Union

Road, Cambridge CB2 1EZ, UK ; Fax: (intrnat.) + 44-1223/336-

1

0

033; E-mail: deposit@ccdc.cam.ac.uk].

2

40B elemental analyzer. Infrared spectra were recorded in KBr

pellets on a Nicolet FT-IR 6700 spectrophotometer. Electronic

absorption spectra were recorded in 1 cm cuvettes on a Shimadzu 70 4.3 Materials and methods for biological tests

1

5

1

60A spectrophotometer. Emission studies in solution and in KBr

54

Culture media were prepared as described previously. Four

disks were performed on a Hitachi F-7000 Fluorometer.

bacterial species were used for the antibacterial screening: E. coli

(

XL1), S. aureus (NCIM 2079), B. subtilis (ATCC 6633), and B.

cereus (ATCC11778). The minimum inhibitory concentration

X-ray quality crystals of compounds 1–7 were grown from 75 (MIC) method uses the progressive double dilution in MMS,

4

.2 X-ray crystal structure determination

2

0

dichloromethane-chloroform and/or methanol solutions. For the

structure determination of 1–2 and 4–7, single crystals of the

respective compounds were mounted on a Bruker Kappa APEX

II diffractometer equipped with a triumph monochromator at

ambient temperature. Diffraction measurements were made using

graphite monochromated Mo Kα radiation. Unit cell dimensions

were determined and refined by using the angular settings of at

which contains the final concentrations of 50, 25, 12, 6, and 3

μg/mL of the complexes. The stock solutions of the complexes

(

10 mg/mL) were prepared by formerly dissolving in DMSO.

For the in vitro evaluation of lipoxygenase inhibition activity,

the reaction mixture contained (final concentration) the test

compounds, dissolved in 25% DMSO at concentrations of 50–

8

9

0

5

0

2

5

00 μM, or the solvent (control), soybean lipoxygenase, dissolved

in 0.9% NaCl solution (250 u/mL) and sodium linoleate (100

μM), in Tris–HCl buffer, pH 9.0. Lipoxidase from Glycine max

(soybean) was used (L7395-15 MU, Sigma) and linoleic acid

sodium salt (L8134-100 MG, Sigma). The reaction was

monitored for 5-15 min at 28ºC, by recording the absorbance of a

conjugated diene structure at 234 nm, due to the formation of 13-

hydroperoxy-linoleic acid. The performance of the assay was

least 100 high intensity (>20(I)) reflections in the range

o

2

0<2<40 . Intensity data were recorded using and  scan

3

4

5

0

5

0

5

0

modes. The frames collected for each crystal were integrated with

5

7

the Bruker SAINT software package using a narrow-frame

algorithm. Data were corrected for absorption using the

5

8

numerical method (SADABS) based on crystal dimensions.

5

9

All structures were solved using the SUPERFLIP package

and refined by full–matrix least-squares method on F using the

CRYSTALS package version 14.40b. All non-disordered non-

hydrogen atoms have been refined anisotropically. For the

disordered non-hydrogen atoms of the tetrafluoro borate and

nitrate anions, occupancy factors were first determined with fixed

55

checked using nordihydroguaiaretic acid as a reference.

2

6

0

4

.4 Computational Details

The geometry of the ligands and all the Cu and Ag cations

was optimized with DFT theory under vacuum conditions and

I

4

3

isotropic displacements. Finally, all them were isotropically 95 without symmetry constraints with the PBE1PBE functional.

4

5

44

refined with fixed occupancy factors. All hydrogen atoms except

the amine ones in 1 were found at the expected positions and

refined using soft constraints. By the end of the refinement, they

were positioned using riding constraints. In the case of 1, both

The 6-31G(d) and SDD basis sets were selected respectively

for the light elements and the metal core. TD-DFT calculations

+

for [Cu(PPh ) (pymtH) ] (1) and [Ag(PPh ) (pymtH)] (7) in

3

2

3 2

the vacuum state were performed on the same level of theory and

the pyrimidino nitrogen atoms in both pyrimidino-thione ligands 100 with the same basis set. In all cases computations were executed

5

6

have been found partially protonated with equal occupation

factors.

with the Gaussian 03W package. Vibrational frequencies

calculations ensured the obtained geometries are real minima in

the potential energy hypersurfaces. Visualization of the obtained

structures and MOs was performed with GaussView 5.0.

X-ray diffraction data for compound 3 were collected by the

6

1

NCS on a Rigaku Saturn 724+ diffractometer. Radiation

source: fine-focus sealed tube. Graphite monochromator, Mo K

6

2

radiation. Profile data from  scans. CrystalClear-SM Expert

was used for cell refinement, data collection and data reduction.

The structure was solved with SHELXS97 and refined with

SHELXL-97. The program used for molecular graphics was

105 4.5 Synthesis of the complexes

I

All Cu complexes were prepared according to the following

6

3

general procedure. In a solution of [Cu(MeCN) ]BF (0.5 mmol)

in 20 mL of CH Cl the appropriate amount of solid

4

2

1

2

|

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Page 13 of 15

New Journal of Chemistry

triphenylphosphine is added (1 mmol for the Cu:PPh

:2:2 or 1.5 mmol for the Cu:PPh :thione = 1:3:1 complexes 60 1479 (s), 1433 (s), 1334 (s, NO ), 1179 (s), 1093 (s), 997 (m),

3

:thione =

=N-H), 3049 (w, =C-H), 1968 (w), 1912 (w), 1618 (s), 1565 (s),

-

1

3

respectively) under stirring. After the solution turns clear the

proper quantity (1 mmol or 0.5 mmol respectively) of the selected

thione dissolved in 20 mL of methanol is added. In the case of

pymtH the final solution was slightly heated. After stirring for 30

742 (s), 693 (s), 514 (s).

5

0

5

0

5

0

5

0

5

0

5

4.5.7 [Ag(PPh

Yellow solid. Yield 95 % (0.48 mmol, 0.38 g). Elemental

S: C, 59.56; H, 4.25; N,

3 2 3

) (pymtH)]NO (7)

min the resulting solutions were filtered and left to stand in air at 65 Analysis: Calcd for C40H34AgN O P

3 3 2

-

1

room temperature after the addition of a small amount of CHCl

3

.

5.21. Found: C, 59.51; H, 4.26; N, 5.23. IR (KBr, cm ): 3120 (w,

=N-H), 3063 (w, =C-H), 1967 (w), 1910 (w), 1602 (s), 1588 (s),

1477 (s), 1433 (s), 1337 (s, NO

743 (s), 693 (s), 517 (s).

Slow evaporation of the solvent gave the products in the form of

crystals which were filtered off and dried in vacuo. Similarly in

the case of silver, the same reactions were performed, only

AgNO₃was used instead. Also only methanol was used as a

solvent.

-

1

2

3

4

5

3

), 1172 (s), 1095 (s), 948 (m),

70

Acknowledgments

4.5.1 [Cu(PPh ) (pymtH) ]BF (1)

3 2 2 4

a) This research has been co-financed by the European

Union (European Social Fund–ESF) and Greek national funds

75 through the Operational Program "Education and Lifelong

Learning" of the National Strategic Reference Framework

Orange solid. Yield 93 % (0.46 mmol, 0.42 g). Elemental

Analysis: Calcd for C H BCuF N P S : C, 58.77; H, 4.26; N,

4

38

4

2

-1

6

=

.23. Found: C, 58.55; H, 4.32; N, 6.21. IR (KBr, cm ): 3122 (br,

N-H), 3071 (w, =C-H), 2853 (w), 1967 (w), 1910 (w), 1601 (s),

(

NSRF) - Research Funding Program: ARCHIMEDES III.

1571 (s), 1480 (s), 1434 (s), 1324 (s), 1179 (s), 1093 (s), 1060 (s,

-

BF ), 985 (m), 743 (s), 694 (s), 516 (s).

Investing in knowledge society through the European Social

Fund.

b) We thank the EPSRC UK National Crystallographic

Service at the University of Southampton for the collection of

the crystallographic data of compound 3.

4

.5.2 [Cu(PPh

3

)

3

(pymtH)]BF

4

(2)

80

Yellow solid. Yield 94 % (0.47 mmol, 0.49 g). Elemental

Analysis: Calcd for C H BCuF N P S: C, 66.39; H, 4.71; N,

5

8

49

4

2

3

-1

2

=

1

.67. Found: C, 66.51; H, 4.68; N, 2.66. IR (KBr, cm ): 3119 (w,

N-H), 3051 (w, =C-H), 2850 (w), 1963 (w), 1913 (w), 1610 (s),

583 (s), 1478 (s), 1434 (s), 1334 (s), 1179 (s), 1091 (s), 1064 (s,

Notes and references

a

-

Aristotle University of Thessaloniki, Department of Chemistry,

br, BF ), 986 (m), 743 (s), 696 (s), 517 (s).

4

8

5

Laboratory of Inorganic Chemistry, P.O.B. 135, GR-541 24 Thessaloniki,

Greece. Fax: +30 2310 997738; E-mail: panpapan@chem.auth.gr,

hatzidim@chem.auth.gr, aslanidi@chem.auth.gr

4

.5.3 [Cu(PPh ) (dmpymtH) ]BF (3)

3 2 2 4

b

Orange solid. Yield 93 % (0.46 mmol, 0.44 g). Elemental

Analysis: Calcd for C H BCuF N P S : C, 60.35; H, 4.85; N,

Aristotle University of Thessaloniki, Department of Chemistry,

Laboratory of Applied Quantum Chemistry, P.O.B. 135, GR-541 24

4

8

46

4

2

-1

90 Thessaloniki,

Greece.

Fax:

+30

2310

997738;

E-mail:

5

.86. Found: C, 60.32; H, 4.88; N, 5.82. IR (KBr, cm ): 3196 (br,

=N-H), 3050 (w, =C-H), 2870 (w), 1970 (w), 1898 (w), 1618 (s),

563 (s), 1480 (s), 1434 (s), 1324 (w), 1231 (s), 1185 (m), 1093

anastp@chem.auth.gr

c

Aristotle University of Thessaloniki, Department of Chemistry,

Laboratory of Biochemistry, P.O.B. 135, GR-541 24 Thessaloniki,

Greece; E-mail: natasa@chem.auth.gr

1

-

(s), 1061 (s, BF ), 998 (s), 747 (s), 695 (s), 517 (s).

4

d

9

5

School of Pharmacy, The Robert Gordon University, Schoolhill,

Aberdeen AB10 1FR, Scotland, United Kingdom. Email:

p.j.cox@rgu.ac.uk

4

.5.4 [Cu(PPh ) (dmpymtH)]BF (4)

3 3 4

Yellow solid. Yield 92 % (0.46 mmol, 0.49 g). Elemental

Analysis: Calcd for C60 S: C, 66.89; H, 4.96; N,

†

Electronic Supplementary Information (ESI) available: crystallographic

H

4 2 3

53BCuF N P

data and refinement details for the isolated complexes (Table S1),

-1

1

00 theoretical structural and energetic data in various media for pymtH and

dmpymtH (Table S2), optimized structures and geometry parameters for

2

.60. Found: C, 66.80; H, 4.91; N, 2.64. IR (KBr, cm ): 3139 (w,

=

N-H), 3051 (w, =C-H), 1967 (w), 1891 (w), 1618 (s), 1563 (s),

I

the studied Ag and Cu cations (Tables S3-S6), NBO atomic charges for

-

1

479 (s), 1433 (s), 1234 (s), 1181 (w), 1091 (s), 1064 (s, br, BF

4

I

the ligands and the studied Ag complexes (Table S7), FMOs of the

optimized stucture of all the studied Cu

I

), 997 (s), 745 (s), 695 (s), 517 (s).

and Ag cations (Table S8),

I

05 normalized absorption spectra of Cu -pymtH complexes and two of the

I

isolated Ag -complexes in dichloromethane (Figure S1), normalized

4

3 3 3

.5.5 [Ag(PPh ) (pymtH)]NO (5)

absoprtion and emission spectra of the ligands in dichloromethane (Figure

S2), normalized emission spectra of all the isolated complexes in

dichloromethane (Figure S3), selected excitations of the

Yellow solid. Yield 92 % (0.46 mmol, 0.49 g). Elemental

Analysis: Calcd for C H AgN O P S: C, 65.17; H, 4.62; N,

5

8

49

3

-1

3.93. Found: C, 65.20; H, 4.59; N, 3.92. IR (KBr, cm ): 3072 (w, 110 [Cu(PPh ) (pymtH) ]BF (1) from TDDFT and simulation of the

3

2

4

=

N-H), 3048 (w, =C-H), 1963 (w), 1910 (w), 1610 (s), 1591 (s),

experimental

absorption

spectrum

(Figure

S4).

See

-

DOI: 10.1039/b000000x/

1

7

478 (s), 1434 (s), 1338 (s, NO

43 (s), 697 (s), 516 (s).

3

), 1177 (s), 1093 (s), 972 (m),

1

2

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4.5.6 [Ag(PPh ) (dmpymtH)]NO (6)

3

Yellow solid. Yield 93 % (0.47 mmol, 0.51 g). Elemental

Analysis: Calcd for C H AgN O P S: C, 65.70; H, 4.87; N,

6

0

53

3

-1

3

.83. Found: C, 65.72; H, 4.85; N, 3.82. IR (KBr, cm ): 3075 (w,

1

25.

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The structural and electronic impact on the photophysical and biological properties of a series of CuI and AgI complexes with triphenylphosphine and pyrimidine-type thiones

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